It is known that telemetry systems can comprise an apparatus that emits optical radiation pulses towards a distant object, and which measures the time that the optical radiation pulses take to reach the object and return to the apparatus. The pulse travel times can then be used to determine the distance of the object. Such devices are known to employ direct detection means to receive the reflected optical radiation.
Further, it is known to modulate the frequency of the emitted optical radiation signal so that optical heterodyne detection means can be employed. Optical heterodyne detection means allow for detection at the quantum noise limit and, as a result, are significantly more sensitive than direct detection means. As such, the use of optical heterodyne detection means minimizes energy requirements while maximizing range, accuracy, and reliability characteristics. An additional advantage of employing optical heterodyne detection means, over direct detection means, is the ability to determine the radial velocity of an object by measuring the Doppler frequency shift.
When using optical heterodyne detection means, it is known to employ an optical system that directs the emitted optical radiation signal towards the distant object, and concentrates the reflected, or return, optical radiation signal for optimal heterodyne detection. The addition of optical polarizing means to such an optical system allows for selective reception of the return optical radiation signal, thereby maximizing the reliability of the optical heterodyne detection means.